Around 250 miles above our heads, people are living and working on board the International Space Station. It is by far the largest structure ever built in space (at least, the part of space we know about) – 250 tons of research modules, life-support systems, solar panels and much, much more.
The construction of the ISS is a huge and expensive project. The joint venture between the US, Russia, Japan, Canada and the European Space Agency began in 1998 and is due to be completed by 2010. But, aside from the mind-blowing construction project itself, simply keeping the space station in business presents a massive challenge.
A fleet of spacecraft is devoted to maintaining and supplying the ISS, delivering new crew-members, bringing astronauts home and ferrying cargo back and forth. These are the private jets, trash cans, trucks and escape modules of space, yet rarely do they attract the attention of the public on the planet below. Rockets may look explosive, but they are just the engines that deliver these craft to the edge of the atmosphere, where the real mission begins.
Of course, everyone has seen the Space Shuttle blast off, as it did once again yesterday morning, taking the first sections of a new Japanese lab to the ISS, along with a pair of new robotic arms. But food, water, oxygen and scientific materials must be delivered too, and the European Space Agency's new Advanced Transfer Vehicle, which blasted off on its maiden voyage this week, is the latest of the cargo ships to enter service. Almost every other month, supplies must be sent up and waste taken away.
A typical crew of three produces 2.6 cubic feet of rubbish every day. Nasa designates two types of material that must be taken off the ISS: trash, consisting of used or defective equipment, spent batteries and so on; and waste, by which it means the detritus from biological experiments and human fecal matter (urine – even the urine of the lab rats – is recycled into drinking water). Whatever it consists of, the rubbish is bagged up and placed into the payload section of one of these space freighters. Unlike manned Shuttle spaceships, the freighters themselves burn up in the Earth's atmosphere along with the waste they carry.
So what are these incredible long-distance lorries? We show the full fleet of the spacecraft that serve manned space missions, along with those on drawing boards around the world.
America's next top gun
As part of America's plan to return to the Moon, the space shuttle fleet will be retired by 2010 and replaced four or five years later by the Orion spacecraft. The craft marks a return to the basic principles of the Apollo spacecraft design that took astronauts to the Moon between 1968 and 1972 – it's not reusable, instead a cone-shaped capsule is designed to splash down in an ocean. Orion will carry a crew of four to six, both to and from the ISS – and maybe the Moon as well. It will be launched by an Ares I rocket, which is based on the existing space shuttle boosters.
The dumper truck
The unsung hero of space flight is the Progress unmanned freighter. A modified version of the Soyuz spacecraft, it is used to re-supply the International Space Station, as it has all previous Russian and Soviet space stations since 1978. Since it needs no bulky life-support systems or heat shields, it can carry a cargo of 2,230kg. Progress typically flies three or four missions a year, with the spacecraft remaining docked with the ISS until just before the next one arrives. The Progress has the ability to raise the ISS's altitude and control the orientation of the station using its thrusters to offset orbit decay. Russia would like to phase out the Progress, replacing it with a craft called Parom ("Ferry"), but funding is a problem.
The H-II Transfer Vehicle is an unmanned craft designed to re-supply the Japanese Experiment Module, which has been built and delivered to the US and is to be added to the ISS. It is larger and simpler than the Progress freighter, having no automatic-docking abilities. Instead, it will move alongside the ISS's Harmony module, where the station's robot arm will grab it and swing it into place. It has a cargo capacity of 7,600kg and will enter service in 2009, being launched by a Japanese-built H-IIB rocket.
Several private companies are proposing to build their own manned spacecraft. Cygnus is one such vehicle, being constructed by the Orbital Sciences Corporation, possibly with a view to replace the Progress freighter – the US has long wanted to cease its reliance on the Russian craft. It will be launched into space by the Taurus II rocket, also being developed by the Orbital Sciences Corporation, some time in 2010.
The shuttle bus
The world's first partially reusable spacecraft, the space shuttle usually carries five to seven people into orbit, but can carry more back to Earth in an emergency. Its first flight was in 1981 and, although each orbiter was designed for 10 years of life, it is still in operation. Six were built. Enterprise, the first, was built as a test vehicle. Columbia has flown 28 missions, Challenger 10 missions, Discovery 34 missions and Atlantis 29 missions. Challenger and Columbia were destroyed by in-flight accidents. Endeavour (20 missions) was built as a replacement for Challenger. Each can carry 24,400kg to low Earth orbit. All Shuttle flights are currently to the ISS, although one is planned to refurbish the Hubble Space Telescope.
Glimpse of the future
Dragon is another design from the private sector. Carrying up to seven astronauts, this spacecraft is the brainchild of a company named SpaceX, and would be placed into orbit by its own rocket, the Falcon 9. It is scheduled to enter service in 2009. There are also proposals for a manned craft built by the European Space Agency, Japan and Russia, and Russian companies are also pursuing a design of their own called Kliper.
Soyuz (shown here next to the space shuttle for scale) is a phrase familiar to amateur space-watchers. Meaning "union", this Russian name is given to the rocket design that has been in service since the Soviet Union dreamt of landing a man on the moon. It was first introduced in 1966. But there is another spacecraft in the Soyuz family. The Soyuz orbiter has launched more manned missions than any other space vehicle. It consists of three parts: a spherical orbital module in which three cosmonauts ride, a small re-entry module used to return them to Earth, and a service module that deploys solar panels for energy. More recently, the orbiter it has found a new role as a lifeboat, permanently docked with the International Space Station. Should anything go seriously wrong, the three crew of the ISS would return to Earth in the Soyuz orbiter. This escape-pod version is one of many Soyuz variants produced, and was partly paid for by Nasa. Its use with the ISS demanded adaptations to allow taller crew members to use it. It first flew in 2002; after the Columbia accident in February 2003, the Soyuz TMA became the only means of transportation for crew members going to and from the ISS. For several years between the retirement of the space shuttle in 2010 and the start of flights by its replacement, the Soyuz TMA will again be the main means of transport, something that is causing growing concern among American politicians.
The ultimate dustbin
The Advanced Transfer Vehicle, built by the European Space Agency, has a payload capacity three times that of the Progress, and can resupply the ISS with fuel, water, air and material for experiments. It will use an automated procedure to dock with the ISS, guided by lasers. After undocking, it burns up in the Earth's atmosphere – along with 6.5 tonnes of rubbish and human waste from the ISS. The first ATV has been named Jules Verne, and a total of seven ATVs could be constructed, each of which will ultimately be incinerated on re-entry. At one stage, the European Space Agency did consider extending the ATV's capabilities, enabling it to carry astronauts, but that idea was shelved in favour of a new, as yet un-named crew-transfer spacecraft being designed along with Japan and Russia. Part of the incentive for a new spacecraft that could carry European astronauts is that Nasa's Orion capsule, unlike the space shuttle it replaces, is being built without European involvement.
China's got cruise control
The Shenzhou spacecraft made its maiden voyage in October 2003, carrying the first Chinese astronaut. A further mission took place in October 2005 with two Chinese astronauts. It is expected to fly again in October with a three-man crew, one of whom will carry out a space walk. In design, it is very similar to the Soyuz, partly due to the practicalities of manned space-flight. For example, only the section that returns to Earth need be clad with a heavy heat-shield. Western analysts believe it is possible for Shenzhou to dock with the International Space Station. China has expressed an interest in being involved in the ISS project, but it is expected that China will soon launch its own first space station, an eight-ton "Space Laboratory" with docking capabilities for the Shenzhou.